Chronic Obstructive Pulmonary Disease (COPD) is a progressive lung disease and includes chronic bronchitis, asthma, and emphysema. Chronic bronchitis is characterized by chronic cough with sputum production. Symptoms of chronic bronchitis such as airway inflammation, mucus hypersecretion, airway hyperresponsiveness, and eventual fibrosis of the airway walls may cause significant airflow and gas exchange limitations. Asthma is similar to chronic bronchitis, though the underlying cause is often an inherent defect of airway smooth muscle or the inflammatory milieu, which makes airway smooth muscle hyper-reactive. Similar to chronic bronchitis, chronic asthma can have similar airway wall thickening, leading to permanent and irreversible airflow obstruction. Emphysema is characterized by the destruction of the lung parenchyma. This destruction of the lung parenchyma leads to a loss of elastic recoil and tethering which maintains airway patency. Unlike the larger airways, bronchioles are not supported by cartilage. This means the bronchioles have little intrinsic support and therefore are susceptible to collapse when loss of tethering occurs, particularly during exhalation.
An acute exacerbation of COPD (AECOPD) is defined by a sudden worsening of symptoms (e.g. increase in or onset of cough, wheeze, and sputum changes) that typically last from several days to a couple of weeks. AECOPD is typically triggered by a bacterial infection, viral infection, allergens, or pollutants that quickly manifest into one or more of airway inflammation, mucus hypersecretion, and bronchoconstriction, which can significantly restrict airways. AECOPD is associated with an increase in morbidity and mortality of COPD patients. Delay in medical treatment for AECOPD can increase the risk of hospitalization for the patient, while prompt medical treatment can prevent worsening conditions and prevent hospitalization. The present inventors have recognized a need for improved monitoring of respiratory function in patients with pulmonary conditions.